The objective of this research program is to test hypotheses related to understanding whether and how the composition of formulas fed, and the feeding practices mothers use, influence young infants'short-term feeding behaviors. The proposed research aims to elucidate potential strategies for optimizing feeding during infancy, which is a first step toward primary prevention of the negative health outcomes associated with undesirable intake and weight gain patterns, such as obesity and type II diabetes. The proposed research builds upon prior research from our laboratory demonstrating that when infants feed protein hydrolysate formula (PHF), which is higher in certain amino acids such as free glutamate, they consume less formula than when feeding cow-milk formulas (CMF), despite showing similar levels of satiation. The primary aim of this research is to test the hypothesis that infants will become satiated faster and will stay satiated longer when feeding formula with higher free glutamate compared to formula with lower free glutamate during infant-led feeding conditions. Feeding during infancy is unique to any other developmental period because infants are entirely dependent on caregivers for what and when they feed;study of infants in isolation of their caregivers creates an incomplete understanding of feeding during infancy. Thus, a secondary aim of this research is to test the hypothesis that, during typical bottle-feeding conditions, the feeding practices of some mothers will override the satiating properties of formulas with high levels of free glutamate. We propose a within-subject design to test our hypotheses. To test our primary hypothesis, we will assess infant consumption during a feed (satiation), latency until a subsequent feed (satiety), and changes in temperature, activity and sleep, in response to feeding PHF, CMF or CMF with added glutamate (CMF+glu) during infant-led feeding conditions, where the infant determines the timing, pace, and duration of the feed. To test our secondary hypothesis, we will assess infant intake and feeding behaviors in response to CMF, PHF and CMF+glu during typical bottle-feeding conditions, in which the mother decides the timing, pace, and duration of the feed. We will then compare feeding during this condition with feeding during the infant-led conditions. Test formulas and feeding conditions will be randomized and counterbalanced across six days of testing. PUBLIC HEALTH RELEVANCE: we know little about influences on and mechanisms underlying infants'developing feeding behaviors. The proposed research will provide important new insights into the role of both internal and external influences on feeding during a developmental period when appropriate intake patterns are especially important for the promotion of optimal growth and development.